Electron beams are used in many industrial processes such as for drying or curing inks, adhesives, paints and coatings. Electron beams are also used for liquid, gas and surface sterilization as well as to clean up hazardous waste.
Conventional electron beam machines employed for industrial purposes include an electron beam accelerator which directs an electron beam onto the material to be processed. The accelerator has a large lead encased vacuum chamber containing an electron generating filament or filaments powered by a filament power supply. During operation, the vacuum chamber is continuously evacuated by vacuum pumps. The filaments are surrounded by a housing having a grid of openings which face a metallic foil electron beam exit window positioned on one side of the vacuum chamber. A high voltage potential is imposed between the filament housing and the exit window with a high voltage power supply. Electrons generated by the filaments accelerate from the filaments in an electron beam through the grid of openings in the housing and out through the exit window. An extractor power supply is typically included for flattening electric field lines in the region between the filaments and the exit window. This prevents the electrons in the electron beam from concentrating in the center of the beam as depicted in graph 1 of FIG. 1, and instead, evenly disperses the electrons across the width of the beam as depicted in graph 2 of FIG. 1.
The drawback of employing electron beam technology in industrial situations is that conventional electron beam machinery is complex and requires personnel highly trained in vacuum technology and accelerator technology for maintaining the machinery. For example, during normal use, both the filaments and the electron beam exit window foil must be periodically replaced. Such maintenance must be done on site because the accelerator is very large and heavy (typically 20 inches to 30 inches in diameter by 4 feet to 6 feet long and thousands of pounds). Replacement of the filaments and exit window requires the vacuum chamber to be opened, causing contaminants to enter. This results in long down times because once the filaments and exit window foil are replaced, the accelerator must be evacuated and then conditioned for high voltage operation before the accelerator can be operated. Conditioning requires the power from the high voltage power supply to be gradually raised over time to burn off contaminants within the vacuum chamber and on the surface of the exit window which entered when the vacuum chamber was opened. This procedure can take anywhere between two hours and ten hours depending on the extent of the contamination. Half the time, leaks in the exit window occur which must be remedied, causing the time of the procedure to be further lengthened. Finally, every one or two years, a high voltage insulator in the accelerator is replaced, requiring disassembly of the entire accelerator. The time required for this procedure is about 2 to 4 days. As a result, manufacturing processes requiring electron beam radiation can be greatly disrupted when filaments, electron beam exit window foils and high voltage insulators need to be replaced.